1. Field of the Invention
This invention relates to adhesive compositions, especially those which are suitable for promoting the bonding of dental restorative materials, especially those that have polymeric components, to tooth enamel, or to tooth dentin or other hard tissues of human body, such as bone. The restorative materials can be polymers, or resins, or can contain polymers or resins in whole, or in part, and comprise materials such as dental composite resins, or methacrylate containing glass ionomer filling materials, or glass ionomer filling materials having ethylenically unsaturated bonds, or they can comprise resin cements.
2. Background of the Invention
The bonding of restorative materials to tooth structure has been an important goal of the dental profession. Such bonding has the benefits of (1) efficiently retaining materials to tooth structure without the need for mechanically locking filling materials into teeth, the latter being a procedure which requires the removal of otherwise healthy tooth structure, and which has been the historical way that materials have been retained, (2) simplifying treatment procedures by eliminating the need for forming precise geometric shapes of teeth when surgical interventions are made, (3) enhancing the quality of interfaces between filling materials by improving the seal between tooth structure and filling materials.
Filling materials in dentistry are generally used to restore teeth to form and function, as well as seal the tooth against oral fluids and bacteria. Directly filling materials are those that are placed in a tooth, and then hardened in the tooth. The most commonly used direct filling polymeric materials are polymer-matrix composite resins, and resin-containing or resin modified glass ionomer filling materials. Compositions for bonding these polymeric materials to tooth structure are especially useful.
Composite resins general comprise a resin matrix, an inorganic filler phase and some coupling agents. The resin matrix generally comprises a monomer system, an initiator system and other stabilizers. The monomer system comprises unsaturated compounds. These compounds generally comprise one or more esters of ethylenically unsaturated carboxylic acids and the adduct of bisphenol A and glycidyl methacrylate (Bis-GMA), such as triethyleneglycol dimethacrylate (TEGDMA), ethyleneglycol dimethacrylate (EGDMA) and 2,2-bis-[4-(2-hydroxy-3-methacrylyloxypropoxy)phenyl]-propane ether (Bis-GMA) in U.S. Pat. No. 3,066,112 to Bowen. Another class of unsaturated materials are urethane dimethacrylates, such as the 1,6-bis(methacrylyloxy-2-ethoxycarbonylamino-2,4,4-trimethylhexane (UEDMA) which is synthesized from 2-hydroxyethyl methacrylate and 2,4,4-trimethylhxamethylenedisocynanate.
When composite resins are placed in a tooth cavity and cured, the hardening (xe2x80x9cpolymerizationxe2x80x9d) of the material usually results in shrinkage. This shrinkage leads to marginal gap formation, allowing for the passage of fluid, bacteria, molecules or ions between the restoration and the cavity wall, which may result in secondary caries, marginal discoloration and pulpal damage. The longevity of the restoration will be reduced by this micro-shrinkage. A strong and permanent bond between the wall of the cavity and the restorative will lead to good sealing, and is beneficial.
Bonding to dental surfaces is usually achieved by the use of acid conditioners, primers and adhesive resins. Primers, which can be applied sequentially, or simultaneously with adhesive resins, generally contain one or more polar groups and unsaturated groups. It is assumed that the polar groups will bond either to the inorganic crystal lattice (apatite) portion of tooth structure, or to the polar part of collagen in the tooth, this occurring by chemical or hydrogen bonding, and/or by micromechanical retention due to the formation of a hybrid layer. The hybrid layer, which has been well characterized, is formed by the infiltration of the primer into a demineralized dentin zone, the demineralization having resulted from acid etching of the tooth. The unsaturated groups of the primer will bond with resin overlayers by free radical polymerization. The polar groups are normally a phosphate, an amino acid or amino alcohol, or a dicarboxylic acid.
U.S. Pat. No. 4,368,043 to Yamauchi, incorporated herein by reference, discloses an adhesive cementing agent for the human body. This agent contains a phosphoric or phosphonic acid ester compound, or a high molecular weight compound obtained by polymerizing the compound whether alone or as co-monomer units.
U.S. Pat. No. 4,514,342 to Billington, incorporated herein by reference, describes an adhesion promoter, suitable for improving the adhesion of composite dental material to tooth enamel. This adhesion promoter contains volatile organic solvent and a polyethylenically unsaturated monophosphate or salt, which contains a monophosphate radical and at least three ethylenically unsaturated groups.
A biologically compatible adhesive is disclosed in U.S. Pat. No. 4,657,941 to Blackwell, incorporated herein by reference. This adhesive is shelf stable as a single component adhesive and includes a mixture of an adhesive promoting and polymerizable monomer system. A free radical polymerizable monomer or prepolymer having ethylenic unsaturation and a phosphorus-containing adhesion promoter, having a free radical polymerization catalyst and an accelerator for the catalyst are included in this system.
While the adhesion between filling materials and enamel or dentin of the tooth is improved by usage of an adhesive promoter, some disadvantages, such as not having great bonding strength, or too great a viscosity for handling of some component exists in some adhesives.
An object of this invention is to provide an adhesive composition, which is suitable for promoting the adhesion of restorative materials to tooth enamel, tooth dentin or other hard tissues of human body.
It is a further object of this invention to provide an adhesive composition which is suitable to be used with other hard tissues of the body.
It is a further object of this invention to provide an adhesive composition, which, when used with other resins, can seal dentinal tubules.
This composition contains a volatile organic solvent and an ethylenically unsaturated monomer and phosphate, which contains a mono-, or di-phosphate radical and at least three ethylenically unsaturated groups.
The preferred solvent is a lower aliphatic alcohol and carbonyl compound. The solution is preferably from 1 to 50% by weight of the total solution of ethylenically unsaturated monomer and phosphate.
The ethylenically unsaturated monomer in the composition is a mono-, di, tri, or multifunctional acrylic monomer, such as 2-hydroxyethyl methacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol dimethacrylate, or 1,4-butanediol divinyl ether.
The ethylenically unsaturated phosphate is the reaction product of alcohol containing unsaturated allyl ether and phosphorus oxychloride or other phosphorus containing compounds.
A very important aspect of this invention are the novel compounds are represented by following formula: 
in which:
R1, is a hydrogen atom, alkyl C1-C6, (preferably C1-C4 when alkyl), or CN,
R is an aliphatic, cycloaliphatic or aryl radical containing from 1 to 10 carbon atoms and having a valence of n+1,
n is an integer from 1 to 5, preferably from 3 to 5, which can be used as a primer for hard tissues.
It has been found, in accordance with the present invention, that the adhesion of filling materials to enamel; or to dentin, may be considerably improved by first applying the composition of this invention to prepared dentin or enamel. The preparation procedure can involve the application of an acid to the tooth surface (where bonding is required), a technique which is known as acid-etching, and which is well known in the dental art. On enamel, the treatment of tooth surfaces with acid preferentially removes inter-rod material, and creates micropores into which the invention, in combination with other resins, can penetrate to form mechanical anchors (tags), when hardened. On dentin, the acid dissolves the mineral phase of dentin, and exposes a fibrillar network of collagen. It is believed that the adhesion results from the penetration of the said composition into the exposed collagen network, and subsequent hardening of the said composition in conjunction with other resins placed as overlayers. These overlayers (known as intermediary resins, or adhesive resins) bond with restorative materials or cements which are subsequently placed on the overlayers.
The adhesive composition, in accordance with this invention, consists of a volatile organic solvent and an ethylenically unsaturated monomer and phosphate, which contains a mono-, or di-phosphate radical and at least three ethylenically unsaturated groups.
The preferred solvent is a lower aliphatic alcohol and carbonyl compounds. The most preferred solvent is acetone. The concentration of the solvent in solution is from 1 to 90% by weight of the total solution of ethylenically unsaturated monomer and phosphate, preferably from 10 to 80% of the total solution of ethylenically unsaturated monomer and phosphate, and most preferably from 30 to 70% by weight.
The ethylenically unsaturated monomer in the composition is a mono-, di, tri, or multifunctional acrylic monomer, such as 2-hydroxyethyl methacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol dimethacrylate, or pentaerythritol triacrylate. The most preferred monomer is 2-hydroxyethyl methacrylate. The concentration of monomer in the composition is from 1 to 60% by weight. The preferred concentration is from 20 to 50% by weight, and the most preferred concentration is from 30 to 40% by weight.
The ethylenically unsaturated phosphate is a reaction product of alcohol containing unsaturated allyl ether and phosphorus oxychlonde or other phosphorus containing compounds.
The unsaturated allyl ether in the phosphate are preferably vinyl groups.
The introduction of phosphate in the composition is very important. It is presumed that the phosphate will interact with inorganic components of a tooth, or other hard tissues, either by forming a complex with the calcium ion or forming a chemical or hydrogen bond with the phosphate, with mineral in enamel, or with mineral that is left in dentin after etching. The phosphate may also be important for interacting with collagen. A very important aspect of this invention is that the new compounds have the following formula: 
in which:
R1, is a hydrogen atom, alkyl C1-C4 or alkyl C1-C6, or CN,
R is an aliphatic, cycloaliphatic or aryl radical containing from 1 to 10 carbon atoms and having a valence of n+1,
n is an integer from 1 to 5, preferably from 3 to 5.
The preferred concentration of phosphate in the composition is from 2 to 70% by weight, although in principle useful results are obtainable in a range of 2-17% by weight. In another aspect, a range of 5 to 40% by weight can be used. The most preferred is from 5 to 10% by weight.
A solution containing the phosphate compound and which is applied to a tooth surface can be hardened simultaneously with resin overlayers which already contain hardening agents. The solution of PTEPAE can also be hardened by the addition of known hardening agents, such as camphorquinone, or benzoyl peroxide.